It is possible to use a single WFSDM for an aeronautical gas turbine engine to serve as both a source of motive power to start the engine and as a source of electrical power driven by the engine. Provided that aeronautical electrical loads that the WFSDM supply as a generator approach the power rating of the WFSDM as a starter motor for the engine, this approach is desirable from the standpoint of weight, cost and reliability.
However, operation of a WFSDM as a starter motor generally requires accurate determination of the position of its rotor to control rotor flux and torque during the starting mode. Most commonly, a rotor position sensor for the WFSDM serves this purpose. Such a position sensor usually comprises an electromechanical shaft position resolver that couples onto the drive shaft of the WFSDM. The resolver may provide relatively accurate absolute angular position information of the drive shaft with suitable exciter electrical excitation and resolver output signal processing. The addition of such a resolver with its associated wiring adds undesirable cost, complexity and unreliability to the system. Various “sensorless” control strategies that eliminate the need for a resolver are available but most are marginal in performance and not inherently robust.